The overall goals of total knee surgery are to implant the components at the required alignments based on defined landmarks and axes, and to achieve the optimal balance of the surrounding soft tissues for the full range of flexion, the purpose being to achieve the best possible durability and function. For example, if the frontal plane alignment results in under-corrected varus, the forces on the medial side can be excessive causing premature wear and loosening. In the sagittal plane, too much extension in the placement of the femoral component relative to the femur can lead to anterior notching and fracture, or a reduction of flexion. Rotational inaccuracy of the tibial component can lead to binding and wear, and patella subluxation.
In general, it has been found that the use of navigation systems has resulted in improved alignments by a reduction of outliers, compared with mechanical alignment systems. This is probably due to the greater consistency of determining the bony landmarks and the definition of the femoral axis using the mechanical axis to the center of the femoral head, rather than the uncertainty of the anatomic axis using present intramedullary rod instruments. Navigation systems include optical tracking systems and electromagnetic tracking systems.
At the ligament balancing stage, navigation used to measure the varus and valgus deviations at different flexion angles has allowed for a more consistent result rather than using blocks with manual non-measured methods. However all systems, whether navigation or mechanical, require the correct definition of the landmarks and axes, and even then errors can occur during the bone cutting procedure itself. An advantage of navigation in this regard is that cuts can be quantitatively checked and corrected if necessary. A limitation of navigation in ligament balancing is that the varus and valgus deviations, while measured accurately, are applied manually with unknown forces. In practical terms, while having many advantages, present navigation systems are expensive, require set-up and skilled maintenance and operation, and add to the operating time.
An alternate measurement system for all steps of the procedure is the use of an instrumented linkage. The mathematical principles for using a succession of links joined by instrumented revolute joints for measuring the coordinate and orientation of the end link relative to the first have been well established (Kinzel et al, 1972; McCarthy, 1990). The application of such spatial linkages to measure joint motions was described, as well as techniques for design configuration and calibration to optimize accuracy (Kirstukas et al, 1992a, 1992b). One example of using calibration procedures showed that accuracies better than 0.2 mm and 0.2 degree could be achieved (Liu and Panjabi, 1996). In a design adapted for biomechanical applications, 1 mm and 1 degree accuracy were obtained (Sholukha et al, 2004).
Instrumented linkages available commercially (Faro Arm; Microscribe) are primarily used for on-site inspection and quality control of engineered parts and assemblies, and for reverse engineering. The Microscribe is however being applied to orthotics and prosthetics fitting, stereotactic registrations, 3-D imaging and MIS surgery, and other procedures.
The present disclosure relates to an instrumented linkage system. The instrumented linkage system may be used in various medical operations, including trauma and surgeries. An exemplary surgical operation is a total knee replacement surgery. Another exemplary surgical operation is a hip replacement surgery. An exemplary trauma operation is locating screws for coupling to an intramedullary rod.
In an exemplary embodiment, the instrumented linkage system is directly attached to an anatomical structure, such as a bone, for example, of a patient. The system may use a digitizing fixture, such as a pointer, to register the anatomical structure with a computer. A cutting guide is then attached to the anatomical structure. The system may then use a paddle inserted in the cut slot of the cutting guide to verify the correct orientation and location of the slot defined by the slotted cutting guide.
In another exemplary embodiment of the present disclosure, a method of placing a cutting guide on at least one bone is provided. The method comprising the steps of affixing a first end of an instrumented linkage system to a substrate; coupling a digitizing fixture to a second end of said instrumented linkage system; digitizing a plurality of points of said at least one bone; locating said cutting guide with said instrumented linkage system; and securing said cutting guide to said at least one bone. In one example, said substrate is a first bone. In another example, said step of affixing a first end of an instrumented linkage system to a substrate includes the steps of coupling a first member of a bone mount to said first bone with a fastener; coupling a second member of said bone mount to said first member of said bone mount; and coupling said second member of said bone mount to said instrumented linkage system. In a further example, said substrate is a patient support and said step of affixing a first end of an instrumented linkage system to a substrate includes the steps of coupling a patient support mount to said substrate; and coupling said instrumented linkage system to said patient support mount. In another example, said step of digitizing a plurality of points of said at least one bone includes the steps of prompting for a first landmark point; receiving an indication that a tip of said digitizing fixture is positioned at said first landmark point; and receiving an indication of a position of each of a plurality of moveable couplings of said instrumented linkage system. In still another example, said step of securing said cutting guide to said at least one bone includes the steps of affixing a frame of said cutting guide to said at least one bone; coupling a paddle fixture to said instrumented linkage system; placing an end of said paddle fixture into a guide member of said cutting guide; adjusting an angular orientation of said guide member relative to said frame based on a determined location of said end of said paddle fixture. In a further example thereof, said step of securing said cutting guide to said at least one bone further includes the steps of locking said angular orientation of said guide member relative to said frame; adjusting a translational position of said guide member relative to said frame based on said determined location of said end of said paddle fixture; and locking said translational position of said guide member relative to said frame.
In another exemplary embodiment of the present disclosure, a method of digitizing a bone is provided. The method comprising the steps of affixing a first end of an instrumented linkage system to said bone; coupling a digitizing fixture to a second end of said instrumented linkage system; providing an indication of when a tip of said digitizing fixture is contacting a first point on said bone; receiving an indication of a position of each of a plurality of moveable couplings of said instrumented linkage system when said tip of said digitizing fixture is contacting a first point on said bone. In one example, said first point is a first landmark point and the method further comprises the step of providing a prompt for said first landmark point so that said tip of said digitizing fixture is contacting a first landmark point on said bone.
In a further exemplary embodiment of the present disclosure, a method of determining a relative motion between a first bone and a second bone. The method comprising the steps of providing an instrumented linkage system, said instrumented linkage system being a passive system; affixing a first end of said instrumented linkage system to a first known location on said first bone; affixing a second end of said instrumented linkage system to a second known location on said second bone; and monitoring a position of each of a plurality of moveable couplings of said instrumented linkage system. In one example, said first bone and said second bone are part of a joint and by monitoring said position of each of said plurality of moveable coupling of said instrumented linkage system a separation of said joint may be determined. In another example, said first known location on said first bone is determined by the steps of: affixing said first end of said instrumented linkage system to said first bone; coupling a digitizing fixture to said second end of said instrumented linkage system; providing for each of a plurality of landmark points an indication of when a tip of said digitizing fixture is contacting a respective landmark point on said first bone; for each respective landmark point, receiving an indication of a position of each of a plurality of moveable couplings of said instrumented linkage system when said tip of said digitizing fixture is contacting said respective landmark point on said first bone; and determining said first known location based on said received indications of said positions of said plurality of moveable couplings. In a further example, said second known location on said second bone is determined by the steps of: affixing said second end of said instrumented linkage system to said second bone; coupling a digitizing fixture to said first end of said instrumented linkage system; and providing for each of a plurality of landmark points an indication of when a tip of said digitizing fixture is contacting a respective landmark point on said second bone; for each respective landmark point, receiving an indication of a position of each of a plurality of moveable couplings of said instrumented linkage system when said tip of said digitizing fixture is contacting said respective landmark point on said second bone; and determining said second known location based on said received indications of said positions of said plurality of moveable couplings.
In still another exemplary embodiment of the present disclosure, an instrumented linkage system for attachment to at least one bone is provided. The system comprising a passive link system including a plurality of links connected together through a plurality of moveable couplings; a first bone mount coupled to a first end of said passive link system; a plurality of separate fixtures each attachable to a second end of said passive link system. Said plurality of separate fixtures including at least two of a second bone mount; a pointer for digitization of said first bone; a saw; and a paddle for accurate placement of at least one cutting guide on said first bone. The system further comprising a processing system operatively coupled to said plurality of moveable couplings to receive indications of a position of each of said plurality of moveable couplings. In one example, said processing system includes an output device which prompts for one of said plurality of fixtures to attach to said second end of said passive link system. In another example, said output device is a display. In still another example, said display provides an indication of said current position of said second end of said passive link system and a target position of said second end of said passive link system. In yet still another example, said display provides an indication of said current orientation of said second end of said passive link system and a target orientation of said second end of said passive link system. In a further example, said output device is supported by said passive link system.
In yet a further exemplary embodiment of the present disclosure, an instrumented linkage system is provided. The system including an arm with a plurality of degrees of freedom and an attachment boss at each end of said arm. Said attachment boss adapted to attach to separate fixtures. Said fixtures including an attachment device for rigid connection to a bone. Said fixtures including a pointer for digitization. Said fixtures including a drill guide for placing of a hole in a bone. Said fixtures including a paddle for accurate placement of a cutting guide on a bone. Said fixtures including an attachment device for rigid connection to a second bone, attached to a second end of said linkage when a first end of said linkage is attached to said bone, to measure the relative motion between said two separate bones.
In still a further exemplary embodiment of the present disclosure, a tool for use with an instrumented link system is provided. The tool comprising a body member having a slot in a first end; and a multi-head tool member coupled to said body member. Said multi-head tool member being received in said slot of said body member and having a first head which includes a digitizing portion and a second head which includes a paddle portion. In one example, said slot is used as a cutting guide.
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode of carrying out the invention as presently perceived.
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the disclosure and such exemplifications are not to be construed as limiting the scope of the invention in any manner.